The present invention relates to optical spectral analysis systems such as spectrographs and monochromators, and more specifically to spectral analysis systems having in-line entrance and exit apertures, a folded optical path comprising a prism and a concave holographic grating and wherein the spectral focal field of the grating is substantially planar over the spectral range of interest.
An instrument that provides an optical separation of light into spectral components is a commonly demanded tool for analytical methodology. Such optical instruments can take the form of spectrographs in which case the light is typically spread spectrally across a photodetector array such an array of diodes with each diode reading the relative intensity of the spectral components in the light for analysis purposes. Alternatively, the instrument can take the form of a monochromator in which a single wavelength or narrow wavelength band is focused at the exit aperture and wherein other wavelengths or bands can be focused thereat by rotating the concave diffraction grating.
Such systems typically find applications in various areas of technology including chemistry, medicine, and physics. As such, the spectral analysis system typically should be placed at an optical output portion of the optical system and an electrical input portion of the electrical or signal processing system. Because of the different demands of the optical and the electrical systems, it is advantageous that their functions be separated and that the spectral analysis system not be of such a configuration as has been true in the past that there fails to exist a clear separation between the optical and the electrical sides.
It is additionally desirable to have an optical instrumentation in which various optical distortions or aberrations are minimized and in which the spectrally separated light is focused at a planar spectral focal field, thereby facilitating the use of planar diode arrays for photo detection.
Compact design and simplicity of operation are also important requirements for such a system allowing it to be easily mounted onto the optical components of the system for precision alignment without intruding the electronics into the optical system itself. Various optical designs for spectrographs, monochromators and other optical analysis instruments exist which fail to achieve some or all of these objectives because of their inefficient optical designs and failure to properly design the spectral separation optics with respect to the remaining spectral instrumentation components.